This invention relates to an automatically guided vehicle which can carry various types of loads along a guide path consisting of guiding materials such as magnetic tape laid in a factory or a warehouse.
Various kinds of automatically guided vehicles which carry loads along preset guide paths in unmanned operation have been invented and put into practice both domestically and abroad. The present applicant has also developed magnetically guided vehicles and provided them for practical use as disclosed in the registered Japan's Utility Model No.3013716 and the Japan's Patent Application No.8-196618.
The magnetically guided vehicle according to the registered utility model No.3013716 cited above has, as shown in FIG. 9, a magnetically guided steering drive unit 3 mounted detachably on the lower surface of the chassis 6 at a position slightly toward the front (near the front wheels 4). This magnetically guided steering drive unit 3 has a magnetic sensor 8 located in front that detects magnetism (magnetic force lines) emitted from the magnetic tape of the guide path, and the drive unit 3 mounted is comprised of a driving wheel 1, a driving motor 2 that drives the driving wheel and an automatic steering device for the driving wheel 1. At the four corners of the lower surface of the chassis 6 wheels 4,4' are attached. The front wheels 4 are universal casters which provide good maneuverability and the rear wheels 4' are direction-fixed. In the rear portion of the chassis 6a battery 31 is mounted, and a control device 32 which governs mainly the automatic control of the magnetically guided steering drive unit 3 is mounted on the lower surface of the magnetically guided steering drive unit 3.
The magnetically guided vehicle according to the application cited above has, as shown in FIG. 10, two magnetically guided steering drive units 3,3, detachably attached to the lower surface of the chassis 6 in an approximately symmetric arrangement, one of which is attached toward the front (near the front wheels) of the chassis 6 and the other which is attached toward the rear (near the rear wheels) of the chassis 6. The two magnetically guided steering drive units 3,3 each have at the front and rear portions magnetic sensors 8a, 8b to detect magnetism (magnetic force lines) emitted from magnetic tape of the guide path. The structure and function of the two magnetically guided steering drive units 3,3 are the same as those described in the cited registered utility model No.3013716. However, with this magnetically guided vehicle, two magnetically guided steering drive units 3,3 are always used for forward and backward running, the guide path being detected by whichever magnetic sensor is positioned in the front with respect to the running direction. For this purpose, universal casters are employed for all of the four wheels at the corners of the lower surface of the chassis 6.
Since the magnetically guided vehicle according to the registered utility model No.3013716 patent cited above (FIG. 9) is so constructed as to be driven and steered by the driving wheels 1 positioned toward the front of the chassis 6, it is practically impossible to steer the vehicle for backward running solely by means of the driving wheels 1 because of the unfavorable relationship among the direction of the driving force exerted by the driving wheels 1, the position of the center of gravity of the vehicle and the direction of running resistance force. The use of this magnetically guided vehicle must, therefore, be limited to cases in which the vehicle runs in one determined direction on a closed-loop path; it cannot be used for running on a complex path that requires the reversing of running direction.
The magnetically guided vehicle according to the application cited above (FIG. 10) allows for both forward and backward running using two magnetically guided steering drive units 3,3. Owing to the two magnetically guided steering drive units 3,3, the vehicle can be driven and steered forcibly in both the forward and backward directions in a perfectly identical manner by detecting the guide path by means of the sensor that is positioned in the front with respect to the running direction, within a certain width without fishtailing. There is, therefore, no problem in using this vehicle on a complex path that requires a combination of forward and backward running modes.
The magnetically guided vehicle of FIG. 10, using two magnetically guided steering drive units 3,3, requires fabrication costs more than twice those for a single magnetically guided steering drive unit. Moreover, the control device for using two magnetically guided steering drive units 3,3 and for synchronized driving inevitably becomes complex. Further, for mounting two magnetically guided steering drive units 3,3, a longer chassis is needed which results in an increased size of the vehicle itself. Still further, even though a control means may be introduced to minimize the trajectory difference between the front and rear wheels, it is inevitable that the minimum width of space needed for running of the vehicle at corners of the path increases, which makes employing the vehicle in a narrow space problematic.
It is the primary object of the invention, therefore, to provide an improved automatically guided vehicle which, while equipped with a single steering drive unit, can run not only in the forward direction but also in the backward direction without any inconvenience.